I admit, I loved the movie and therefore bought the book, because I thought if the movie is that amazing, what's the book going to be!
To my astonishment, the plots of those two differ a lot. But that's okay.
I quite liked The Prestige (book). The way you experience the world of magic in the early 20th century out of the perspectives of two revalling magicians is absolutely brilliant. You learn about magic tricks and stage illusions through the eyes of the two greatest illusionists of that time, each one frequently sabotaging the other one's performances and trying to steal their secrets.
It is incredibly entertaining to read (also due to all those nice and sweet British terms which I adore!) and it is one of those books where you have to stay focused to follow the plot and to find all the little hints and cross references - which I also adore!
Furthermore it has this awesome atmosphere of the unknown - of magic and illusions in which you get lost soon after starting to read.
There's this story that frames the narration of the magicians and this story is very hard and annoying to read in the beginning, because it's mostly boring talk about genealogy in which neither the protagonist is interested in, nor is all the information actually necessary for the plot (the crucial information could also be summarized in two or three phrases). There's a nice and thrilling turn in the end, but because of the needless boring beginning, I rate The Prestige 4/5 stars.